In anionic polymerization systems, since active hydrogen compounds such as water and alcohol, oxygen, or the like become polymerization inhibiting substances, which deactivate the growing terminal anions or initiators, the control of anionic polymerization under the presence of these materials is known to be difficult.
On the other hand, when producing a polymer having a high molecular weight of, for example, several tens of thousands or more by an anionic polymerization method, since the more attempts are made to obtain polymers having high molecular weights, the more the concentration of the growing terminal anion in the polymerization solution reduces, relative effects of polymerization inhibiting substances increase greatly and the growing terminal anion becomes prone to deactivation. For this reason, there has been a problem in that the production of polymers having a desired molecular weight is difficult and yields of targeted polymers are reduced.
In order to solve such problems, a method is proposed where benzylmagnesium bromide, butyllithium, or the like is added to monomers or solvents to be used to react with the polymerization inhibiting substances containing active hydrogen, which are contained in the monomers or the solvents in trace amounts, and the polymerization inhibiting substances are removed from the monomers or the solvents for purification.
In this method, there is a need to add an excessive amount of benzylmagnesium bromide, butyllithium, or the like in order to completely remove the polymerization inhibiting substances. However, since there are also some cases where these reagents function as polymerization inhibitors or polymerization initiators, they must be removed completely from the monomers or solvents before the polymerization. For this reason, there was a practically problem when carrying out anionic polymerization on an industrial scale, since there were some cases where the purification process or the like became complex, and moreover, monomers partially polymerized at the time of purifying the monomers by a distillation method or the like caused a reduction of the purification recovery factor of the monomers.
Moreover, Hsieh et al. reports on the anionic polymerization of styrene or dienes at room temperature by having an ate complex of sec-butyllithium or polystyryl anion and dibutylmagnesium as a polymerization initiator and Sawamoto et al. reports on the styrene bulk polymerization at a polymerization temperature of 120° C. using n-butyllithium/dibutylmagnesium complex. However, even in these examples using dibutylmagnesium, precise control of the molecular weight of a high molecular weight polymer has not been achieved (see Non-patent documents 1 to 4).
[Non-patent document 1] H. L. Hsieh et al., Macromolecules, 1986, 19, 299
[Non-patent document 2] Seitz, L., Little, G. F., J. Organomet. Chem., 1969, 18, 227
[Non-patent document 3] A. Deffieux, et al., Macromol. Chem., 1999, 200, 621
[Non-patent document 4] 7th SPSJ International Polymer conference, 27A13 (1999)